The Periodic Table

@GaurangTandon how should we determine that whose Hydrogen will be lost? For example if I have ortho hydrroxybenzoic acid, will the hydrogen of Hydroxy or that of COOH be lost?

Gaurang Tandon

@Abcd whichever is better acid will be lost

if you have two moles base, then both will be lost

Abcd

@GaurangTandon or is it based on -I effect

COOH shows better -I effect

so it's Hydrogen should not be lost

otherwise there will be "too" much negativity

Gaurang Tandon

carboxylic acid is without doubt much more acidic than hydroxyl group....

Abcd

1:21 PM

oops, yes

due to resonance

Resonance> I effect

Gaurang Tandon

haven't you been taught all this yet? or are you skipping ahead of your class?

Abcd

@GaurangTandon Self study.... organic course couldn't be finished in FIITJEE due to time constraint. Now we have our holidays till 25th march and I gotta complete all this myself :/

Did you go to any coaching @GaurangTandon ?

Gaurang Tandon

@Abcd what place are you dude? this is ridiculous. o-chem will be the base for you in 12-th. There's so much in it.

you just can't leave it due to "time constraint". it's great that you're doing it all youtself

@Abcd i went to resonance

Abcd

@GaurangTandon will I be able to complete 11th portion in 10 days (organic)?

Gaurang Tandon

@Abcd depends on your other priorities and how much is still left

Abcd

1:25 PM

@GaurangTandon I am done with isomerism, and almost done with GOC.

Gaurang Tandon

@Abcd i meant maths and phy

Abcd

@GaurangTandon Physics almost done, just left with waves, fluids and full class 11th revision. Maths though ><.

12th Maths chapters are much better and fun.

11th maths sucked.

Gaurang Tandon

@Abcd only you can tell if you'll be able to finish it or not; make a timetable, note which books to study from, and do it

Abcd

@GaurangTandon Do you know why o Hydroxy benzoic acid is stronger acid than p isomer? The reason written is intramolecular hydrogen bonding in ortho isomer but I believe that there can be **intermolecular ** hydrogen bonding in the para isomer ...

Gaurang Tandon

ortho effect

could be, let me think agai

read this - quora.com/…

Hbond stabilizes the anion

Abcd

1:36 PM

@GaurangTandon Yup, but my point is:

that there can be intermolecular Hydrogen bonding in the para isomer's anion

Why don't people take that into account?

orthocresol

@RinSam

2 days ago, by orthocresol

Please do not flag homework questions for moderator attention. The mod attention flag should be reserved for cases which can only be dealt with using moderator powers, or for cases where moderator judgment is required. Possible responses to homework questions include voting to close and/or downvoting, neither of which are moderator-only actions. The correct flag to use is: should be closed > off-topic > homework.

Thanks.

Gaurang Tandon

@Abcd I dunno if that'll be so effective

intramolecular is much much stronger

Abcd

@GaurangTandon Well, I just read that inter is stronger.

Here:

4

Q: Strength of intramolecular vs intermolecular hydrogen bonds

Why are intramolecular hydrogen bonds weaker than intermolecular hydrogen bonds?

Is it worth asking this on main?

Gaurang Tandon

whoops gotta think abt that again

@Abcd i've always wondered why you're so scared of asking on main

just add your relevant effort and post, no worries :)

@Abcd do add this thing into your question

Tanuj

@M.A.R. What's up troll king?

M.A.R.

1:44 PM

up

Adverb: up (not comparable)

Away from the surface of the Earth or other planet; in opposite direction to the downward pull of gravity.
I looked up and saw the airplane overhead.
(intensifier) Used as an aspect marker to indicate a completed action or state Thoroughly, completely.
I will mix up the puzzle pieces.
Tear up the contract.

(14 more not shown…)

Tanuj

@M.A.R. Yea you're normal :)

Abcd

@GaurangTandon Ah, okay.

RinSam

2:02 PM

@orthocresol @orthocresol Sorry, I'm relatively new to SE and I'd suggest an option exclusively for that (more stuff of the wrong 'homework' kind ruling SE)

Abcd

@GaurangTandon can you remove the credit?

Gaurang Tandon

@Abcd yeah sure if you wish to

removed

Abcd

thanks

Gaurang Tandon

welcome

@Abcd "internal hydrogen bonding between the OH− and COO−" is it OH- or simply OH?

Abcd

@GaurangTandon OH

Gaurang Tandon

2:17 PM

the COOH loses a proton to form COO-. But how do you form OH-?

then edit your post to OH

good

Abcd

@GaurangTandon 1 or 2 months ago, was there spam downvoting going on at Chem.SE? I haven't seen any SE site with so many downvotes...

Gaurang Tandon

I only became active here in the past month or so, so I really don't know exactly; but I guess the questions are sometimes so poor that downvotes have to be used

that said, SE has a strong system in place to monitor any spam downvotes

and moderators know what's happening, they have the data to monitor every spam voting pattern; and can revert any such attempts

so have faith in Chem.SE mod team :)

Abcd

Ok

Zhe

@GaurangTandon You can up/down vote anything you like

There's no requirement for that

Gaurang Tandon

@Zhe well why would I wish to downvote good posts or upvote bad posts :P

Zhe

2:27 PM

¯\_(ツ)_/¯

M.A.R.

2:43 PM

@Abcd WTH is spam downvoting?

Well, for one thing, we're no way as hell as forgiving as Math.SE regarding crappy questions.

And you seem to come from there.

@GaurangTandon that's at best uptight, and suggesting you should use downvotes more.

@GaurangTandon but, what you consider a bad post could be considered good by someone else, and vice versa.

Abcd

@M.A.R. even Physics.SE doesn't have so many downvotes.

There was a question I remember

It was asked on both Chem and Phys

It received numerous upvotes on Physics.SE

and 5 downvotes here and it was even closed here.

M.A.R.

Everyone has the right to vote however they want, as long as it's not targeted at someone.

Abcd

AFAIR, it was regarding orbital visulaisation.

@M.A.R. hmm.

M.A.R.

What is your point?

Abcd

my point is downvoting should be reduced here, especially for new users.

They will get scared.

M.A.R.

2:48 PM

If it was received the same way, it would be pointless to have both Chem and physics.

Zhe

That sounds like a situation where the chemists thought it was a bad chemistry question and the physicists thought it was a good physics questions

Abcd

Its better to guide them.

Zhe

@Abcd If you want to do that, go right ahead

M.A.R.

If you feel there's a problem, you should back it up with hard data.

I do not think we downvote excessively.

@Abcd why? Downvoting doesn't mean "you suck", it means "your post sucks"

orthocresol

@RinSam I appreciate your concerns, but the flagging options aren’t something the moderators can change. There is already a way to flag for homework, anyway.

M.A.R.

2:51 PM

RinSam what he said.

Abcd

@M.A.R. and @Zhe I certainly didn't mean to demean the efforts of Chem.SE mods. Hope you didn't misinterpret.

Zhe

I'm not a mod, so whatever you said didn't demean me

My opinion of whether or not questions are good isn't swayed by whether a user is new

I rarely up or down vote questions, but I do vote a lot on answers

M.A.R.

@Abcd I'm not a mod. And downvoting has nothing to do with mods. But I just think you should provide evidence if you hope anything will come of your claims

Plus, I wouldn't criticize a system I don't fully understand.

Abcd

@M.A.R. Okay.

M.A.R.

@Zhe that's exactly how voting should ideally be

You don't see the user, just the content they're providing

I might downvote a new user's post and leave a nice comment explaining the policy to them.

Gaurang Tandon

3:11 PM

@M.A.R. nope, I did not mean to suggest using downvotes more often; if you think, I did, I am sorry and mark it as a correction

M.A.R.

@GaurangTandon no, I mean you really should downvote more

Gaurang Tandon

@M.A.R. if you're specifically talking about me, I have my own rules of downvoting stuff ;) i only downvote questions when (1) it is a user with >30 rep and didn't use mathjax; not even put the dollar sign (2) does not respond to clarification attempts even after a day (though it gets closed by that time) (3) blatantly offtopic. I only downvote answers when they are completely wrong and I can verify that they are wrong. And I always let the poster know about this through commenting/upvoting

...an existing comment about the same issue

M.A.R.

So bureaucratic

I have my own rules of downvoting things too:

1) when it is a question that's not useful to the site and future visitors.

I might also downvote just because I wanna.

That covers it up

Wow, Linear, I dig the new avatar

Then again, I couldn't see your avatar for like a decade

Abcd

@GaurangTandon Are you free for 5 minutes?

Gaurang Tandon

@Abcd just wait five mins

Abcd

3:20 PM

Okay, please ping me when you are free.

Gaurang Tandon

@Abcd ok say

Abcd

@GaurangTandon I don't get why methanol is more acidic than water. I saw this:

13

Q: Why is methanol more acidic than water?

Methanol is slightly more acidic than water. Their $\mathrm{p}K_\mathrm{a}$ values, in water, are $15.5$ and $15.7$, respectively. All other aliphatic alcohols, however, are less acidic than water. Is the following reasoning correct? This is my best rationalization; is there anything better or ...

acid-base water

There's an answer there but since I do not know MO theory, I couldn't understand it.

However, the last paragraph of the answer is somewhat interpretable.

Gaurang Tandon

@Abcd know what Abcd, I really like your questions, because your every question teaches me something new, something that wasn't taught in my class

Abcd

Cool :-).

Gaurang Tandon

yeah :D I'm reading that answer right now, will tell ya when I understand

look, i'll admit I don't know what anionic hyperconj is and I will have to read about it first now

Abcd

3:27 PM

@GaurangTandon that anionic HC part is for stability is DSM ...

Linear Christmas

@M.A.R. Thank you for the compliment

Abcd

@GaurangTandon see the last paragraph of the answer, that one is of our purpose , acidity in aqueous solution

Linear Christmas

it was what came up in a picture search for 'algebraic geometry'

Gaurang Tandon

@LinearChristmas it's an extended penrose triangle i'd say

@Abcd ah yes checking it out

Linear Christmas

also interesting that you noticed soon after you changed your own avatar @M.A.R.

@GaurangTandon I really have no idea beyond what I searched, so I won't comment

Gaurang Tandon

3:31 PM

@LinearChristmas sorry I was referring to MAR's profile pic

Linear Christmas

Ah, I see

Gaurang Tandon

@Abcd I read that now. I understood everything except "but because methanol is intrinsically more acidic due to its polarizability, it is still slightly more acidic than water, even in aqueous solution. " I feel so dumb right now...

^-- what is ringo trying to mean by that text I highlighted in bold?

I thought over it, I've no clue

Abcd

@GaurangTandon Yuo, this was the part that confused me.

@GaurangTandon Is it that the +I effect of the methyl group increases the bond polarity

And then there are stabilising ion-dipole interactions

Morrison boyd states:

Rick

wait a minute, shouldn't pka of water be 14?

Gaurang Tandon

@Rick you're not the only one saying so ;) read the comments on that post

Abcd

3:43 PM

"Alcohols are weaker acids than water in solution- which is where we are normally concerned with acidity- and this is a solvation effect, a bulky group interferes with ion dipole interactions"-Morrison Boyd

@Rick pKa+ pKb of water = 14

Does that ring anything @GaurangTandon? The explanation from morrison boyd?

Gaurang Tandon

@Abcd no it doesn't

@Abcd well, the resulting carbanion (CH3O-) is being destabilized by the +I of methyl; I don't know how that helps increase acidity of methanol :/

Abcd

@GaurangTandon its increasing the dipole atleast, and then there are stabilising ion-dipole interactions.

Rick

Gaurang Tandon

@Abcd OKay. But, what about ethanol?

@Rick but we just now know methanol more acidic than water?

Abcd

@GaurangTandon "too much" negativity due to +I effect, plus two methyl groups interfere in the stabilising ion dipole interactions

Rick

3:50 PM

This is all that NCERT says :P

Abcd

@Rick See the question on SE, plus its given in Morrison Boyd as well as LG Wade that methanol is more acidic

Gaurang Tandon

@Abcd yeah that makes some sense now; more than what ringo said

whaddya say @Rick? About Abcd's expanded explanation of what ringo said

Abcd

@GaurangTandon But I need someone's verification and certification before passing this explanation to my friends.

Rick

I don't know, I just found this:

pubs.acs.org/doi/abs/10.1021/acs.jchemed.6b00623

Organic chemists generally defend the use of these values by citing measurements of the equilibrium constant for the water + methoxide acid–base reaction that suggested that methanol (pKa = 15.54) is a stronger acid than water; from this, organic chemists have concluded that pKa of water must be 15.74 rather than 14.00. Here we discuss the problems that invalidate this conclusion,

Gaurang Tandon

@Abcd I think you basically detailed what ringo said

Abcd

3:58 PM

@Rick that's another question

maybe you should ask that on main

Right now the point is:

If water has pka 15.7

then it is less acidic than methanol

And we are looking for reasons for that.

Gaurang Tandon

@Rick that's a great find actually; if you've free time till tomorrow, you might actually wanna read it in full; might have some good info; or i'll give it a shot but after boards

@Abcd exactly. I think the ones you gave corroborate with those by ringo

Avatar Shiny

Why is methanol more acidic than water?

Dear sirs I walked googling for the S-H O-H

Thing instead I found a link on Quora

Which explained the ROH and H20 thing

Basically carbon is more EN than H

Datz y

Zhe

@AvatarShiny This question isn't quite clear enough. In water? In themselves?

Abcd

@Zhe In aqueous solution.

We have been discussing this for long.

Rick

so 15.7 is obtained if we have [H2O] in the denominator,and actually take it's concentration,but in reality, it's activity should be taken as 1, this should give 14

Gaurang Tandon

4:07 PM

@Rick i'd suggest you read that paper

Avatar Shiny

What's wrong with this?

14

Q: Why is methanol more acidic than water?

Methanol is slightly more acidic than water. Their $\mathrm{p}K_\mathrm{a}$ values, in water, are $15.5$ and $15.7$, respectively. All other aliphatic alcohols, however, are less acidic than water. Is the following reasoning correct? This is my best rationalization; is there anything better or ...

acid-base water

Rick

@AvatarShiny There are two problems now, we don't understand MO theory well enough, so we're trying to explain it in simpler terms like inductive effect, and we aren't sure if that statement is correct or not. 😅

Abcd

@AvatarShiny Nothing is wrong with it. The last paragraph is of our concern which isn't clear and I just posted my explanation for it above.

Gaurang Tandon

ethanol is less acidic due to "too much" negativity due to +I effect, plus two methyl groups interfere in the stabilising ion dipole interactions

Abcd

@Rick No, not knowing MO theory isn't the reason.

Gaurang Tandon

4:12 PM

methanol is more acidic than water as the +I effect is increasing the dipole, and then there are stabilising ion-dipole interactions.

(i reposted Abcd's msgs)

Avatar Shiny

Read clayden once HOMO LUMO has been given really really really well

Abcd

@AvatarShiny Thanks for informing, but is it pertinent to the pertaining discussion?

Avatar Shiny

@Abcd But that's how they have explained H2O and CH3OH

Abcd

@AvatarShiny Dude, the solvent is different

The solvent for MO theory explanation is DMSO

DMSO = Dimethyl sulfoxide

What concerns us is the acidity in WATER.

Avatar Shiny

Yup

Abcd

4:18 PM

And only the last paragraph of the answer is dedicated to it.

Avatar Shiny

That's been answered through two factors

1. Why deprotonation is favorable for Ch3OH

2. It's small size makes the stabilization through hydrogen bonding nearly the same as H2O

Point one is through HOMO Lumo

M.A.R.

4:39 PM

@GaurangTandon extended triangles are also known as squares

Gaurang Tandon

@M.A.R. ofc they are :P

M.A.R.

4:53 PM

Guys, I might or might not be AFK the next couple of weeks beginning on Saturday due to transplant. If you needed to ping someone, ping @ortho. He's so pingable.

Linear Christmas

@M.A.R. giving or receiving?

M.A.R.

Receiving

Linear Christmas

want some TIPS?

he he

M.A.R.

punching Linear

Linear Christmas

I wouldn't do that

you know they pump up priority patients

so if you hurt me too badly, I might get the transplant before you

M.A.R.

4:57 PM

Face transplant?

Mine's not the same queue. It's OK. I can punch you.

Linear Christmas

You should ask your doctor if punching is limited to the hitting in the face by definition

not sure it is

M.A.R.

Well, it's your face I'm gonna punch

Rick

@LinearChristmas @M.A.R. ortho hydroxy benzoic acid more acidic than the para isomer because of H bonding, right?

why do we not consider intermolecular H bonding?

Linear Christmas

@M.A.R. That's fair

Rick

The question is from here: chemistry.stackexchange.com/questions/91076/…

orthocresol

5:25 PM

@GaurangTandon You know you can delete your own comments.

Linear Christmas

@Rick I don't really know but I wouldn't correlate intermolecular H-bonds with acidity in water

it's probably a poor correlation even after inductive effects are considered

intramolecular H-bonds are another matter

to look for a qualitative answer (assuming there is one in this case), I would start with searching all pKa's of the three hydroxybenzoic acids

(for steps 1 and 2)

then pKa's for phenol, benzoic acid and perhaps salicylic acid

Rick

5:44 PM

@LinearChristmas hmmm...but why?

oh ok..you said you're not sure

Linear Christmas

("perhaps salicylic acid" -> more substituted salicylic acid)*

@Rick Your question is fundamentally about why one effect is numerically bigger than some other; I don't know how to answer this from first principles with a qualitative discussion

An intermolecular hydrogen bond would be the nth to consider; if this were otherwise, HF would be more acidic than HCl, NH3 would be more aciding than HCl and so on

Rick

6:01 PM

ok that example makes it more clear

Linear Christmas

Well yes, but just to be sure it's not an explanation, just an example you are probably more familiar with

Linear Christmas

6:36 PM

Here are some pKa's for similar compounds

still looking for k-methyl-n-hydroxybenzoic acids and k-t-butyl-n-hydroxybenzoic acids

(table headings: molecule, pKa1, temperature of measurement; pka2; temperature of measurement; reference)

Rick

7:16 PM

@LinearChristmas so from the data, intermolecular h bonding is not considered a major factor in acidic strength?

Zhe

7:38 PM

@Rick As an exercise, at 1 M what is the expected number of non solvent neighbors?

Rick

7:52 PM

@Zhe I don't know what's the exact way to calculate the probability, but I think that would mean 1 mole of the organic compound in 1 L of water (=55.5 moles) , so around 1 in 55?

Zhe

@Rick Does it seem like that would affect acidity very much?

Rick

No, not much. If at all, maybe from the solvent, but that will affect both equally. I guess the acidic order might be very different in solid state then?

Abcd

Is this MO diagram for methanol given in Clayden, correct?

I don't see any C-C bond in methanol, so why has author shown it?

I guess its just a misprint

Rick

@Zhe but even such low probabilities cause huge differences in boiling points such as in o and p nitrophenol? I just confused myself with the last comment, will water affect the acidity, in the para compound?

Zhe

@Rick Not in solution they don't...

@Abcd There must be some mistake. Either you're wrong or they're wrong. They are too many disconnects

Rick

8:05 PM

The H in H2O will form hydrogen bonds?

Zhe

I'm not sure what that has to do with the boiling point of a pure substance that's not in aqueous solution...

Rick

Oh ok...we take the pure substance there, ok

but does water affect acidity in the para compund, the H20 nearby can form H bonds..

Zhe

well, solvent effects are huge in acidity so yes

it's not clear exactly what that would be

After all, the solvent is the thing that's stabilizing your conjugate base

Rick

but ortho hydroxy benzoic acid is more acidic than para hydroxy benzoic acid

i guess the solvent effect doesnt affect this

Abcd

8:23 PM

In a nucleophile and electrophile reaction, if the electrons interact with $\sigma*$ orbital, then why is the bond that breaks a $\sigma$ one?

Similarly, if electrons interact with $\pi*$ orbital, then the bond that breaks is $\pi$ orbital one.

I can see symmetry but whats the reason?

Oh, I got it.

2 in sigma and 2 in sigma* will mean no bond.

Rick

@Zhe so is it safe to say that although different solvents will cause changes in acidity, ortho hydroxy benzoic acid will remain more acidic than para hydroxy benzoic acid

or even in water

Zhe

9:29 PM

@Rick I don't think so

Chemistry is not a simple subject. We have emergent complexity that you frequently just cannot predict

2

Well, I guess it depends on what you mean by "safe"

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